Brain enzyme caught doing something unexpected—it builds polysialic acid on itself

A chance discovery at Nagoya University in Japan has shown that a well-known brain enzyme has a hidden ability: It builds a sugar chain on itself, becomes secreted from the cell and deactivates, then switches on outside the cell once the chain is removed. The finding, published in the Journal of Biological Chemistry, overturns a decades-old assumption about how polysialic acid, a sugar chain critical for brain development and function, is produced and shows a new way an enzyme can regulate its own activity.